Subject: Re: [PATCH net-next 3/3] selftests: traceroute: Add ICMP extensions tests

From: Willem de Bruijn <[email-masked]>
Date: Wed, 22 Oct 2025 18:12:13 -0400

Ido Schimmel wrote:
> Test that ICMP extensions are reported correctly when enabled and not
> reported when disabled. Test both IPv4 and IPv6 and using different
> packet sizes, to make sure trimming / padding works correctly.
> 
> Disable ICMP rate limiting (defaults to 1 per-second per-target) so that
> the kernel will always generate ICMP errors when needed.

This reminds me that when I added SOL_IP/IP_RECVERR_4884, the selftest
was not integrated into kselftests. Commit eba75c587e81 points to

https://github.com/wdebruij/kerneltools/blob/master/tests/recv_icmp_v2.c

It might be useful to verify that the kernel recv path that parses
RFC 4884 compliant ICMP messages correctly handles these RFC 4884
messages.

But traceroute parsing the data is sufficient validation that packet
generation is compliant with the RFCs.

> Reviewed-by: Petr Machata <[email-masked]>
> Signed-off-by: Ido Schimmel <[email-masked]>
> ---
>  tools/testing/selftests/net/traceroute.sh | 280 ++++++++++++++++++++++
>  1 file changed, 280 insertions(+)
> 
> diff --git a/tools/testing/selftests/net/traceroute.sh b/tools/testing/selftests/net/traceroute.sh
> index dbb34c7e09ce..a57c61bd0b25 100755
> --- a/tools/testing/selftests/net/traceroute.sh
> +++ b/tools/testing/selftests/net/traceroute.sh
> @@ -59,6 +59,8 @@ create_ns()
>  	ip netns exec ${ns} ip -6 ro add unreachable default metric 8192
>  
>  	ip netns exec ${ns} sysctl -qw net.ipv4.ip_forward=1
> +	ip netns exec ${ns} sysctl -qw net.ipv4.icmp_ratelimit=0
> +	ip netns exec ${ns} sysctl -qw net.ipv6.icmp.ratelimit=0
>  	ip netns exec ${ns} sysctl -qw net.ipv6.conf.all.keep_addr_on_down=1
>  	ip netns exec ${ns} sysctl -qw net.ipv6.conf.all.forwarding=1
>  	ip netns exec ${ns} sysctl -qw net.ipv6.conf.default.forwarding=1
> @@ -297,6 +299,142 @@ run_traceroute6_vrf()
>  	cleanup_traceroute6_vrf
>  }
>  
> +################################################################################
> +# traceroute6 with ICMP extensions test
> +#
> +# Verify that in this scenario
> +#
> +# ----                          ----                          ----
> +# |H1|--------------------------|R1|--------------------------|H2|
> +# ----            N1            ----            N2            ----
> +#
> +# ICMP extensions are correctly reported. The loopback interfaces on all the
> +# nodes are assigned global addresses and the interfaces connecting the nodes
> +# are assigned IPv6 link-local addresses.
> +
> +cleanup_traceroute6_ext()
> +{
> +	cleanup_all_ns
> +}
> +
> +setup_traceroute6_ext()
> +{
> +	# Start clean
> +	cleanup_traceroute6_ext
> +
> +	setup_ns h1 r1 h2
> +	create_ns "$h1"
> +	create_ns "$r1"
> +	create_ns "$h2"
> +
> +	# Setup N1
> +	connect_ns "$h1" eth1 - fe80::1/64 "$r1" eth1 - fe80::2/64
> +	# Setup N2
> +	connect_ns "$r1" eth2 - fe80::3/64 "$h2" eth2 - fe80::4/64
> +
> +	# Setup H1
> +	ip -n "$h1" address add 2001:db8:1::1/128 dev lo

nodad or not needed in this lo special case?

> +	ip -n "$h1" route add ::/0 nexthop via fe80::2 dev eth1
> +
> +	# Setup R1
> +	ip -n "$r1" address add 2001:db8:1::2/128 dev lo
> +	ip -n "$r1" route add 2001:db8:1::1/128 nexthop via fe80::1 dev eth1
> +	ip -n "$r1" route add 2001:db8:1::3/128 nexthop via fe80::4 dev eth2
> +
> +	# Setup H2
> +	ip -n "$h2" address add 2001:db8:1::3/128 dev lo
> +	ip -n "$h2" route add ::/0 nexthop via fe80::3 dev eth2
> +
> +	# Prime the network
> +	ip netns exec "$h1" ping6 -c5 2001:db8:1::3 >/dev/null 2>&1
> +}
> +
> +traceroute6_ext_iio_iif_test()
> +{
> +	local r1_ifindex h2_ifindex
> +	local pkt_len=$1; shift
> +
> +	# Test that incoming interface info is not appended by default.
> +	run_cmd "$h1" "traceroute6 -e 2001:db8:1::3 $pkt_len | grep INC"
> +	check_fail $? "Incoming interface info appended by default when should not"
> +
> +	# Test that the extension is appended when enabled.
> +	run_cmd "$r1" "sysctl -w net.ipv6.icmp.errors_extension_mask=0x01"
> +	check_err $? "Failed to enable incoming interface info extension on R1"
> +
> +	run_cmd "$h1" "traceroute6 -e 2001:db8:1::3 $pkt_len | grep INC"
> +	check_err $? "Incoming interface info not appended after enable"
> +
> +	# Test that the extension is not appended when disabled.
> +	run_cmd "$r1" "sysctl -w net.ipv6.icmp.errors_extension_mask=0x00"
> +	check_err $? "Failed to disable incoming interface info extension on R1"
> +
> +	run_cmd "$h1" "traceroute6 -e 2001:db8:1::3 $pkt_len | grep INC"
> +	check_fail $? "Incoming interface info appended after disable"
> +
> +	# Test that the extension is sent correctly from both R1 and H2.
> +	run_cmd "$r1" "sysctl -w net.ipv6.icmp.errors_extension_mask=0x01"
> +	r1_ifindex=$(ip -n "$r1" -j link show dev eth1 | jq '.[]["ifindex"]')
> +	run_cmd "$h1" "traceroute6 -e 2001:db8:1::3 $pkt_len | grep '<INC:$r1_ifindex,\"eth1\",mtu=1500>'"
> +	check_err $? "Wrong incoming interface info reported from R1"
> +
> +	run_cmd "$h2" "sysctl -w net.ipv6.icmp.errors_extension_mask=0x01"
> +	h2_ifindex=$(ip -n "$h2" -j link show dev eth2 | jq '.[]["ifindex"]')
> +	run_cmd "$h1" "traceroute6 -e 2001:db8:1::3 $pkt_len | grep '<INC:$h2_ifindex,\"eth2\",mtu=1500>'"
> +	check_err $? "Wrong incoming interface info reported from H2"
> +
> +	# Add a global address on the incoming interface of R1 and check that
> +	# it is reported.
> +	run_cmd "$r1" "ip address add 2001:db8:100::1/64 dev eth1 nodad"
> +	run_cmd "$h1" "traceroute6 -e 2001:db8:1::3 $pkt_len | grep '<INC:$r1_ifindex,2001:db8:100::1,\"eth1\",mtu=1500>'"
> +	check_err $? "Wrong incoming interface info reported from R1 after address addition"
> +	run_cmd "$r1" "ip address del 2001:db8:100::1/64 dev eth1"
> +
> +	# Change name and MTU and make sure the result is still correct.
> +	run_cmd "$r1" "ip link set dev eth1 name eth1tag mtu 1501"
> +	run_cmd "$h1" "traceroute6 -e 2001:db8:1::3 $pkt_len | grep '<INC:$r1_ifindex,\"eth1tag\",mtu=1501>'"
> +	check_err $? "Wrong incoming interface info reported from R1 after name and MTU change"
> +	run_cmd "$r1" "ip link set dev eth1tag name eth1 mtu 1500"
> +
> +	run_cmd "$r1" "sysctl -w net.ipv6.icmp.errors_extension_mask=0x00"
> +	run_cmd "$h2" "sysctl -w net.ipv6.icmp.errors_extension_mask=0x00"
> +}
> +
> +run_traceroute6_ext()
> +{
> +	if ! traceroute6 --help 2>&1 | grep -q "\--extensions"; then
> +		log_test_skip "traceroute6 too old, missing ICMP extensions support"
> +		return
> +	fi
> +
> +	setup_traceroute6_ext
> +
> +	RET=0
> +
> +	## General ICMP extensions tests
> +
> +	# Test that ICMP extensions are disabled by default.
> +	run_cmd "$h1" "sysctl net.ipv6.icmp.errors_extension_mask | grep \"= 0$\""
> +	check_err $? "ICMP extensions are not disabled by default"
> +
> +	# Test that unsupported values are rejected.
> +	run_cmd "$h1" "sysctl -w net.ipv6.icmp.errors_extension_mask=0x80"
> +	check_fail $? "Unsupported sysctl value was not rejected"
> +
> +	## Extension-specific tests
> +
> +	# Incoming interface info test. Test with various packet sizes,
> +	# including the default one.
> +	traceroute6_ext_iio_iif_test
> +	traceroute6_ext_iio_iif_test 127
> +	traceroute6_ext_iio_iif_test 128
> +	traceroute6_ext_iio_iif_test 129
> +
> +	log_test "IPv6 traceroute with ICMP extensions"
> +
> +	cleanup_traceroute6_ext
> +}
> +
>  ################################################################################
>  # traceroute test
>  #
> @@ -437,6 +575,145 @@ run_traceroute_vrf()
>  	cleanup_traceroute_vrf
>  }
>  
> +################################################################################
> +# traceroute with ICMP extensions test
> +#
> +# Verify that in this scenario
> +#
> +# ----                          ----                          ----
> +# |H1|--------------------------|R1|--------------------------|H2|
> +# ----            N1            ----            N2            ----
> +#
> +# ICMP extensions are correctly reported. The loopback interfaces on all the
> +# nodes are assigned global addresses and the interfaces connecting the nodes
> +# are assigned IPv6 link-local addresses.
> +
> +cleanup_traceroute_ext()
> +{
> +	cleanup_all_ns
> +}
> +
> +setup_traceroute_ext()
> +{
> +	# Start clean
> +	cleanup_traceroute_ext
> +
> +	setup_ns h1 r1 h2
> +	create_ns "$h1"
> +	create_ns "$r1"
> +	create_ns "$h2"
> +
> +	# Setup N1
> +	connect_ns "$h1" eth1 - fe80::1/64 "$r1" eth1 - fe80::2/64
> +	# Setup N2
> +	connect_ns "$r1" eth2 - fe80::3/64 "$h2" eth2 - fe80::4/64

Stray IPv6 addresses in this IPv4 test?

As a matter of fact, is it feasible to merge the IPv4 and IPv6 tests
with some basic variables like $TRACEROUTE, $SYSCTL_PATH and $ADDR?

(I appreciate that you spent more time looking at that, fine to leave
if it is not practical to do so.)

> +
> +	# Setup H1
> +	ip -n "$h1" address add 192.0.2.1/32 dev lo
> +	ip -n "$h1" route add 0.0.0.0/0 nexthop via inet6 fe80::2 dev eth1
> +
> +	# Setup R1
> +	ip -n "$r1" address add 192.0.2.2/32 dev lo
> +	ip -n "$r1" route add 192.0.2.1/32 nexthop via inet6 fe80::1 dev eth1
> +	ip -n "$r1" route add 192.0.2.3/32 nexthop via inet6 fe80::4 dev eth2
> +
> +	# Setup H2
> +	ip -n "$h2" address add 192.0.2.3/32 dev lo
> +	ip -n "$h2" route add 0.0.0.0/0 nexthop via inet6 fe80::3 dev eth2
> +
> +	# Prime the network
> +	ip netns exec "$h1" ping -c5 192.0.2.3 >/dev/null 2>&1
> +}
> +
> +traceroute_ext_iio_iif_test()
> +{
> +	local r1_ifindex h2_ifindex
> +	local pkt_len=$1; shift
> +
> +	# Test that incoming interface info is not appended by default.
> +	run_cmd "$h1" "traceroute -e 192.0.2.3 $pkt_len | grep INC"
> +	check_fail $? "Incoming interface info appended by default when should not"
> +
> +	# Test that the extension is appended when enabled.
> +	run_cmd "$r1" "sysctl -w net.ipv4.icmp_errors_extension_mask=0x01"
> +	check_err $? "Failed to enable incoming interface info extension on R1"
> +
> +	run_cmd "$h1" "traceroute -e 192.0.2.3 $pkt_len | grep INC"
> +	check_err $? "Incoming interface info not appended after enable"
> +
> +	# Test that the extension is not appended when disabled.
> +	run_cmd "$r1" "sysctl -w net.ipv4.icmp_errors_extension_mask=0x00"
> +	check_err $? "Failed to disable incoming interface info extension on R1"
> +
> +	run_cmd "$h1" "traceroute -e 192.0.2.3 $pkt_len | grep INC"
> +	check_fail $? "Incoming interface info appended after disable"
> +
> +	# Test that the extension is sent correctly from both R1 and H2.
> +	run_cmd "$r1" "sysctl -w net.ipv4.icmp_errors_extension_mask=0x01"
> +	r1_ifindex=$(ip -n "$r1" -j link show dev eth1 | jq '.[]["ifindex"]')
> +	run_cmd "$h1" "traceroute -e 192.0.2.3 $pkt_len | grep '<INC:$r1_ifindex,\"eth1\",mtu=1500>'"
> +	check_err $? "Wrong incoming interface info reported from R1"
> +
> +	run_cmd "$h2" "sysctl -w net.ipv4.icmp_errors_extension_mask=0x01"
> +	h2_ifindex=$(ip -n "$h2" -j link show dev eth2 | jq '.[]["ifindex"]')
> +	run_cmd "$h1" "traceroute -e 192.0.2.3 $pkt_len | grep '<INC:$h2_ifindex,\"eth2\",mtu=1500>'"
> +	check_err $? "Wrong incoming interface info reported from H2"
> +
> +	# Add a global address on the incoming interface of R1 and check that
> +	# it is reported.
> +	run_cmd "$r1" "ip address add 198.51.100.1/24 dev eth1"
> +	run_cmd "$h1" "traceroute -e 192.0.2.3 $pkt_len | grep '<INC:$r1_ifindex,198.51.100.1,\"eth1\",mtu=1500>'"
> +	check_err $? "Wrong incoming interface info reported from R1 after address addition"
> +	run_cmd "$r1" "ip address del 198.51.100.1/24 dev eth1"
> +
> +	# Change name and MTU and make sure the result is still correct.
> +	# Re-add the route towards H1 since it was deleted when we removed the
> +	# last IPv4 address from eth1 on R1.
> +	run_cmd "$r1" "ip route add 192.0.2.1/32 nexthop via inet6 fe80::1 dev eth1"
> +	run_cmd "$r1" "ip link set dev eth1 name eth1tag mtu 1501"
> +	run_cmd "$h1" "traceroute -e 192.0.2.3 $pkt_len | grep '<INC:$r1_ifindex,\"eth1tag\",mtu=1501>'"
> +	check_err $? "Wrong incoming interface info reported from R1 after name and MTU change"
> +	run_cmd "$r1" "ip link set dev eth1tag name eth1 mtu 1500"
> +
> +	run_cmd "$r1" "sysctl -w net.ipv4.icmp_errors_extension_mask=0x00"
> +	run_cmd "$h2" "sysctl -w net.ipv4.icmp_errors_extension_mask=0x00"
> +}
> +
> +run_traceroute_ext()
> +{
> +	if ! traceroute --help 2>&1 | grep -q "\--extensions"; then
> +		log_test_skip "traceroute too old, missing ICMP extensions support"
> +		return
> +	fi
> +
> +	setup_traceroute_ext
> +
> +	RET=0
> +
> +	## General ICMP extensions tests
> +
> +	# Test that ICMP extensions are disabled by default.
> +	run_cmd "$h1" "sysctl net.ipv4.icmp_errors_extension_mask | grep \"= 0$\""
> +	check_err $? "ICMP extensions are not disabled by default"
> +
> +	# Test that unsupported values are rejected.
> +	run_cmd "$h1" "sysctl -w net.ipv4.icmp_errors_extension_mask=0x80"
> +	check_fail $? "Unsupported sysctl value was not rejected"
> +
> +	## Extension-specific tests
> +
> +	# Incoming interface info test. Test with various packet sizes,
> +	# including the default one.
> +	traceroute_ext_iio_iif_test
> +	traceroute_ext_iio_iif_test 127
> +	traceroute_ext_iio_iif_test 128
> +	traceroute_ext_iio_iif_test 129
> +
> +	log_test "IPv4 traceroute with ICMP extensions"
> +
> +	cleanup_traceroute_ext
> +}
> +
>  ################################################################################
>  # Run tests
>  
> @@ -444,8 +721,10 @@ run_tests()
>  {
>  	run_traceroute6
>  	run_traceroute6_vrf
> +	run_traceroute6_ext
>  	run_traceroute
>  	run_traceroute_vrf
> +	run_traceroute_ext
>  }
>  
>  ################################################################################
> @@ -462,6 +741,7 @@ done
>  
>  require_command traceroute6
>  require_command traceroute
> +require_command jq
>  
>  run_tests
>  
> -- 
> 2.51.0
>